1. Field of the Invention
The present invention relates to a method for numerical position control of at least two shafts, each motordriven In particular, the present invention relates to a method of control of at least two shafts in hobbing machines, with the position of each shaft being adjustable by an input of desired position values via a control loop associated with that shaft that includes a speed control section. There is at least one master shaft and at least one slave shaft with a given transmission ratio with respect to the master shaft and which is controllable synchronously with the rotation of the master shaft. Each shaft can be fitted with a workpiece or tool.
2. Related Art
For Various machining techniques, as for example in gearcutting by hobbing or in shaping by the generating process, it is necessary to move one machine shaft as a function of the movements of one or several other machine shafts. To this end different transmission ratios between the various shafts must be selectable.
Methods in which the rotary movements of motor-driven shafts can be regulated in a manner dependent on one another are referred to also as "electronic transmissions".
European Patent Application 0 184 036 A1 which corresponds to U.S. Pat. No. 4,695,960, discloses a numerical o control of an electronic transmission for machine tools for producing gears. According to the disclosure the movement of the workpiece is made to be dependent on at least one movement of the tool in such a way that a reference variable for a position control loop of the workpiece is derived from the actual position of the tool.
In the manufacture of high-precision parts, as is the case with the production of gears by hobbing methods, the s synchronism of the respective motor-driven shafts must meet stringent requirements. However, if, as in the above named European patent application, the desired reference variable for use in the position control loop of one shaft is derived only from the actual position of the tool, i.e. from the actual position of one of the other shafts, the tool shaft, this necessarily results in a certain lag of the first shaft relative to the tool shaft. The reason for this is that the first shaft receives its desired value only from the actual value of the tool shaft, i.e. only after a rotation of the tool shaft has been executed. While this lag can be minimized by appropriate measures, it can never be kept at zero because the system design introduces the lag.